I came across this online paper, entitled Subjective Time vs. Proper (Clock) Time by Ronald P. Gruber, Stanford University, in which the following statement can be found:
The shorter the latency of the person’s response or the more bits (or chunks) a person processes during a time period, the faster is the person’s information-processing rate.
Information-processing rate would decrease with age, and account for the common feeling of time moving by faster in later decades of life.
The other important factor in the subjective measure of time would be the cummulative items of information processed:
(1) subjective time is based upon the overall information-processing rate, and
(2) the subjective experience of life’s duration is related to if not based upon the total information processed (cumulative uncertainty).
I don't know if there have been any serious studies on the topic, but in trying to comprehend what the paper is saying two things come to mind:
The healthy awake human mind is constantly "thinking," and often in a chaotic, random way, influenced by incessant visual, auditory and other external stimuli, as well as loose associative chains moving forwards (future) and backwards (past). This process is effortless, and at many points slips into a semi-conscious level, barely detectable. It tends to recur, be interrupted, and wander far away from its point of origin; a random walk or "scattered thoughts."
However, when effort, concentration or interest in a challenging mental activity focuses the mind, a structure arises within the featureless fabric of thoughts, forming nodes of "achievement", such as solving a problem, or understanding a concept, achieving a milestone, etc. The mind is again prone to the same types of distractions; however, these nodes of convergence become an internal metronome. Let's call this type of thinking "recurrent concentration."
It is the preponderance of these second "states of mind" in people that opt to further their education with challenging courses, write a book, or teach a difficult topic (as examples of demanding tasks) that introduces the punctuation marks in the otherwise effortless flow of conscience. By doing so, an internal clock is awoken, and the passage of time slows down - an internal structure with compartments is created with its own architecture and distinct spaces.
Here would be an illustration of the two types of "thinking":
Notice that this has nothing to do with Daniel Kahneman's dual process theory. Rather it acknowledges the teachings in Zen, or in Mindfulness Theravada Buddhist meditation regarding the existence of a "monkey mind" that wanders off all the time, and needs to be gently reminded to focus. See, for instance Fig.25 on page 111 of Zen Training: Methods and Philosophy by Katsuki Sekida:
Also, there would be an apparent contradiction only at a superficial level: engaging in effort-full activities would sharpen our concentration at the expense of our perception of the passage of time ("being in the zone"); yet it would be the decision to initially engage in something new, and the subsequent intermediate and ultimate achievements resulting from directed mind focus on challenging tasks that would leave a biographic mark in the person, effectively highlighting a particular period, and creating texture in the passage of time. It would, hence, become conscious only in retrospect.
Finally, this take would be more along the lines of cumulative information along a biography, and in particular, "challenging" periods of acquiring information with effort, and less dependent on the more neuronal or biological processing rate.
The question is:
What is the status of research on the topic of subjective perception of time as accelerating towards later decades of an individual, and in particular, in connection to my thoughts expressed above.